Reinforcing bar and method for the production thereof

ABSTRACT

The invention relates to a reinforcing bar for mineral building materials, particularly for cement. The inventive reinforcing bar ( 10 ) is made of a bar of plastic material reinforced by fiber, which has a central, elongate core ( 12 ) and several ribs ( 14 ) which extend along the length of the core, which are disposed at an angular distance from each other, which form a cross or a star in the cross section thereof and which are twisted around the core axis ( 16 ) in a helical manner.

The invention relates to a reinforcing bar for mineral-based buildingmaterials, especially concrete, and a method for manufacture thereof.

Building components such as, for example, ceilings or supports, mustcarry compressive, tensile, and shearing forces. So such buildingcomponents generally are manufactured from steel-reinforced concrete orprestressed concrete. Concrete is subject to compressive loading andsteel is subject to tensile loading. Up to now, the bars or wiresrequired for reinforcement of concrete have been mainly manufacturedfrom steel. For this purpose, steel has the advantage that it ischemically compatible with concrete. A disadvantage, however, is thesusceptibility to corrosion by rusting. When rust appears, the concreteseparates from the reinforcing bar, so damage and deterioration canoccur. This means that steel-reinforced concrete constructions must beregularly inspected and repaired.

In order to avoid this, it has already been suggested to coat the steelwith synthetic resin, for example with epoxy resin. However, it has beenshown that when the synthetic resin coating is damaged, pitting occursat rust spots and progresses rapidly. Another disadvantage of coatedsteel reinforcement is the poor adhesion between the concrete and thereinforcement. The form-locking fit to the surface ribs of thereinforcing bars is not sufficient because of the faulty adhesive fit.

Therefore the aim of the invention is to develop a reinforcing bar formineral-based building materials, especially for concrete, that issimple to manufacture and that can be securely anchored in the buildingmaterial, and that can be transported and installed without risk ofdamage.

The combinations of features recited in the independent claims areproposed to achieve this aim. Advantageous embodiments and furtherdevelopments of the invention are recited in dependent claims.

A concept essential to the invention is that the reinforcing bar isformed by means of a fiber-reinforced plastic strand which has a longcentral core and several spaced-apart ribs oriented at an angle to oneanother along the entire length of the core and having star-shaped orcross-shaped cross section, that are each helically twisted all aroundthe core axis. The ribs of the strand at the same time convenientlyproject beyond the surface of the core by at least one rib width equalto the core diameter. A form-fitted anchoring of the reinforcing bar inthe concrete results from the helical winding of the ribs. In order tobe able to carry the desired tensile forces, at least some of thereinforcement fibers are formed as longitudinal fibers that runcontinuously along the strand and are aligned parallel to the axis inthe core region and in the direction of the pitch of the ribs in the ribregion. The individual reinforcement fibers formed as longitudinalfibers in the rib region in this case conveniently run at a constantdistance from the core axis.

In order to enable reliable handling of the reinforcing bars at theconstruction site, the strand is additionally reinforced, at least inthe region of the ribs, with transverse or circumferential fibers. Thetransverse fibers prevent buckling or sagging of the grooves between theribs when the reinforcing bars are piled on top of one another duringtransport and during use. When the bars are piled on top of one another,contact points are formed at sufficiently short intervals by means ofthe helically twisted ribs to make sure that no deformation occurs underload. The latter is also important in the assembled state, if thereinforcing bars are laid in a criss-cross pattern. While thelongitudinal fibers in the reinforcing bars have the function of tensionreinforcement, the transverse fibers have the function of bucklingreinforcement. In a preferred embodiment of the invention, the ribs ofthe strand are oriented at identical angles to one another and the ribsare twisted with a constant pitch. However, in principle it is alsopossible for the ribs to be twisted along the strand with variablepitch. The pitch angle of the ribs relative to the core axis can beadjusted over relatively broad limits and can be optimized. It isconveniently between 15° and 75°, preferably 30° to 50°.

The longitudinal and transverse fibers conveniently form a fiber fabricor crossply. The reinforcement fibers are advantageously selected fromthe group of carbon fibers, glass fibers, aramid fibers, high-strengthpolyethylene fibers, basalt fibers, natural fibers, or from a mixture ofthose fibers. The reinforcement fibers in the near-surface region of thestrand are conveniently selected as carbon fibers because of chemicalcompatibility with concrete, while less expensive glass fibers and thelike can also be used in deeper layers of the strand interior.

The plastic matrix of the strand may be made of a thermosetting plasticpolymer material, preferably from the group of epoxy resin, polyesterresin, vinyl resin. In order to enable easier deformation of the strandduring the manufacturing process, it may be advantageous for the plasticmatrix to consist of a thermoplastic, preferably from the group ofpolyamide (PA), polymethylmethacrylate (PMMA), polyphenylene sulfide(PPS), polypropylene (PP), polyethylene terephthalate (PET),polybutylene terephthalate (PBT), polyetherimide (PEI), styrene polymer(ABS), polyetheretherketone (PEEK).

The method for manufacture of the reinforcing bars according to theinvention essentially involves helically twisting and cutting intolengths a fiber-reinforced plastic strand with star-shaped orcross-shaped cross section.

In principle, in this case it is possible to embed a fiber or fabriccore into the plastic strand during its manufacture by a pultrusionprocess (strand drawing).

For manufacture of the plastic strand according to the invention, it ispreferred for a prefabricated sheet, ribbon, or tubular startingmaterial made from fiber-reinforced plastic to be reshaped, preferablyfolded, to form a strand with cross-shaped or star-shaped cross section,and to then be helically twisted and cured. In this case it isespecially advantageous if sheet, ribbon, or tubular material,containing a thermoplastic as a binder matrix, is reshaped into thefiber-reinforced plastic strand using pressure and heat. In manufactureof the fiber reinforcement, at least two layers made from differentfiber materials can be used in the sheet, ribbon, or tubular startingmaterial, where an outer layer conveniently consists of carbon fibers.

The invention is explained in more detail in the following with the helpof schematically represented exemplary embodiments in the drawing. Thedrawing shows

FIGS. 1 a and 1 b a schematic representation of a reinforcing bar withcross-shaped cross section, before and after helical twisting;

FIGS. 2 a through 2 c sheet or ribbon shaped starting material (FIG. 2a) and tubular starting material (FIG. 2 b) for manufacture of a twistedreinforcing bar with cross-shaped cross section (FIG. 2 c), in aschematic partial cutaway view.

The reinforcing bars represented in the drawing are intended forreinforcement of concrete building components.

Reinforcing bar 10 is made up of a fiber-reinforced plastic strand whichhas a long central core 12 and several spaced-apart ribs 14 oriented atan angle to one another along the entire length of the core and havingstar-shaped or cross-shaped cross section. The starting material is, forexample, the strand shape 10′, the ribs 14 thereof are helically twistedaround core axis 16 in the same direction and with the same pitch inorder to form the reinforcing bar shown in FIG. 1 b. Some of thereinforcement fibers are formed as longitudinal fibers 18. In the finalproduct as in FIG. 1 b, longitudinal fibers 18 run parallel to the coreaxis 16 in the core region, while in the region of the ribs 14 they runparallel to the ribs and so are aligned in the direction of the pitch ofribs 14. The individual longitudinal fibers 18 in the rib region are aconstant distance from core axis 16 over their entire length. Thepurpose of longitudinal fibers 18 inside reinforcing bar 10 isespecially to carry tensile forces. Twisting ribs 14 of the strandresults in a stable form-locking fit inside the concrete which, in spiteof the otherwise smooth surface of the reinforcing bar, preventsreinforcing bar 10 from loosening its bond with the surroundingconcrete.

Other reinforcement fibers 20 run inside the strand shape, essentiallytransverse to longitudinal fibers 18. This is also the case in theregion of ribs 14. Transverse fibers 20 provide buckling reinforcementthat can carry shearing forces acting on reinforcing bar 10, in order toreduce the risk of buckling. In the exemplary embodiment shown in FIG. 1b, the pitch angle of ribs 14 relative to core axis 16 is about 30° to40°. Since there are a total of four ribs here, when the reinforcingbars are stacked on top of one another there are sufficiently shortsupport lengths between two bearing points, which oppose sagging underload or during use.

FIGS. 2 a to 2 c schematically indicate that sheet or ribbon shapedstarting material 10″ (FIG. 2 a) or tubular starting material 10′″ (FIG.2 b) can also be used to manufacture reinforcing bars with across-shaped cross section.

There are various options for manufacture of sheet or ribbon shapedstarting material 10″. In the “rolltrusion” process, individualfilaments, fabric, or crossply are pre-impregnated and passed through aroller press. As a result, a thin ribbon is produced that is just toothin for the purposes relevant here. So several ribbons must be laid ontop of one another and bonded together by heating and melting. As aresult, ribbons with different reinforcing cores, such as carbon fiberor glass, can also be used. Ribbons prefabricated in this way are thenheated, folded into a cross, and helically twisted. A disadvantage ofthis process is the relatively slow production rate. Also onlyhigh-quality thermoplastics such as polyamides can be used for thebinder matrix.

Another option for manufacture of sheet material is for prefabricatedfabric and crossply to be impregnated with a binder and fed to a doubleband press. The fabric or crossply can be a combination of differentfibers and can be made relatively thick.

As a result, a continuous sheet material 10″ is obtained that atelevated temperature can be, for example, deformed into the desiredcross shape and twisted. The difference from the rolltrusion process isthe fact that we begin with a finished fabric and crossply withsufficient wall thickness, so that several sheets do not have to beassembled together to make a multilayer system. In this case,thermoplastics can be used as binders from the group of polyamide (PA),polymethylmethacrylate (PMMA), polyphenylene sulfide (PPS),polypropylene (PP), polyethylene terephthalate (PET), polybutyleneterephthalate (PBT), polyetherimide (PEI), styrene polymer (ABS),polyetheretherketone (PEEK). In the double band press, the material isfirst heated up and then cooled down gradually over the length of thepress, so that an already cured material comes out at the end. Anessential advantage of the method is the high production rate. Thevariety of fibers and binder materials that can be used also permitscost optimization.

There are likewise various options for manufacture of tubular startingmaterials as in FIG. 2 b:

In the pultrusion process (strand drawing), impregnated continuousfibers are pultruded over a mandrel. This can be done in several steps,where crosswinding can also be carried out following each process step.In this case, a tube 10′″ with longitudinal and transverse fibers isobtained, where the fibers also can be made from different materialssuch as, for example, carbon fibers outside and glass inside. The tubeis then subsequently heated, pressed into a cross, and twisted.

Impregnated braided tubing made from the desired fiber material can alsobe used for manufacture of tubes 10′″ as in FIG. 2 b. Braided tubes arefirst manufactured in braiding machines in the form of a fiber tube andthen impregnated with binder.

The impregnated tube is then again pressed into a cross shape andtwisted. In principle, it is also possible to first deform the braidedtubing into a cross shape and to only then impregnate it.

In summary, we can say the following: The invention relates to areinforcing bar for mineral-based building materials, especiallyconcrete. Reinforcing bar 10 according to the invention is made up of afiber-reinforced plastic strand which has a long central core 12 andseveral spaced-apart ribs 14 oriented at an angle to one another alongthe entire length of the core and having star-shaped or cross-shapedcross section, that are helically twisted around core axis 16.

1. Reinforcing bar for mineral-based construction materials, especiallyconcrete, comprising a fiber-reinforced plastic matrix strand includinga long central core and several spaced-apart ribs oriented at an angleto one another along an entire length of the core and having astar-shaped cross section or a cross-shaped cross section, the ribsbeing helically twisted around an axis of the core, the strand beingreinforced by (1) individual longitudinal fibers at least in a ribregion that run at a constant distance from the axis of the core and (2)transverse fibers at least in the rib region.
 2. Reinforcing bar as inclaim 1, wherein at least some of the individual longitudinal fibers runcontinuously along the strand and are aligned parallel to the axis in acore region and in the direction of the twist of the ribs in the ribregion.
 3. Reinforcing bar as in claim 1, wherein the ribs of the strandare oriented at identical angles to one another.
 4. Reinforcing bar asin claim 1, wherein the ribs of the strand are twisted along the strandwith a constant pitch.
 5. Reinforcing bar as in claim 1, wherein theribs of the strand are twisted along the strand with variable pitch. 6.Reinforcing bar as in claim 1, wherein a pitch angle of the twist of theribs of the strand relative to the core axis is 15° to 75°. 7.Reinforcing bar as in claim 1, wherein the ribs of the strand projectbeyond the surface of the core by at least one rib width equal to thecore diameter.
 8. Reinforcing bar as in claim 1, wherein reinforcementfibers comprise at least one of carbon fibers, glass fibers, aramidfibers, high-strength polyethylene fibers, basalt fibers, or naturalfibers.
 9. Reinforcing bar as in claim 8, wherein the reinforcementfibers, at least in a near-surface region of the strand, are carbonfibers.
 10. Reinforcing bar as in claim 1, wherein the longitudinalfibers and the transverse fibers form a fiber fabric or crossply. 11.Reinforcing bar as in claim 1, wherein the plastic matrix of the strandis made from thermosetting plastic polymer material.
 12. Reinforcing baras in claim 11, wherein the thermosetting plastic polymer materialcomprises at least one of an epoxy resin, a polyester resin or a vinylresin.
 13. Reinforcing bar as in claim 1, wherein the plastic matrix ofthe strand is made of a thermoplastic.
 14. Reinforcing bar as in claim13, wherein the thermoplastic comprises at least one of polyamide,polymethylmethacrylate, polyphenylene sulfide, polypropylene,polyethylene terephthalate, polybutylene terephthalate, polyetherimide,styrene polymer, or polyetheretherketone.
 15. Reinforcing bar as inclaim 1, wherein a pitch angle of the twist of the ribs of the strandrelative to the core axis is 30° to 50°.
 16. Reinforcing bar as in claim1, wherein the ribs of the strand project beyond the surface of the coreby at least one rib width equal to twice the core diameter.